The present invention pertains generally to assembly systems, particularly of the type including conveyors defining a path of travel between workstations for conveying of a workpiece to one or more workstations along the path of travel, and more particularly the present invention pertains to a lowerator mechanism for raising and lowering a workpiece with respect to a workstation.
In automotive production lines, it is generally known to transport individual workpieces, such as automotive body panels, frame components, etc., to and between workstations where selected operations, such as welding, are performed by workers, robots, or other processing equipment. Transporting individual workpieces to, and accurately placing the workpieces at, a desired workstation on a production line poses numerous difficulties. Tooling and other processing equipment at a workstation present obstacles that must be avoided by the incoming and departing workpieces. After reaching any given workstation, the workpieces must be accurately positioned within the workstation so that the necessary processing operations can be performed. The efficiency considerations of modern production lines and the like demand that workpiece delivery to a workstation be as rapid as possible.
In many common production lines and other assembly applications, workpieces are transported along an overhead rail, for instance a monorail. Motor-driven trolleys travel along the rail to and between various workstations. Electrical conductors can be provided along the rail to provide power to the trolley motors. The trolleys carry workpieces along the path defined by the rail, delivering the workpieces to the workstations.
To perform a processing operation on a workpiece transported along an overhead rail, some mechanism must be provided to raise and lower the workpiece with respect to the workstation. Prior known mechanisms for raising and lowering a workpiece into the workstation have moved the entire workpiece-laden trolley along with an entire section of the overhead rail. This type of mechanism is complicated in design and prone to mechanical failures. For example, joints must be provided between the fixed and moveable rail sections for the electrical conductors responsible for powering the trolleys. It can be difficult to ensure that the section of rail lowered with the trolley is properly realigned with the fixed rail sections. If the conductors of the lowerable and fixed rail sections become misaligned, unreliable or faulty system operation can result. This negatively impacts the operational capacity of the production or assembly lines, for instance by causing wasteful xe2x80x9cdown-timexe2x80x9d for repairs. In addition to the foregoing disadvantages, the prior known mechanisms cycle at relatively slow speeds, since the weight of the carrier, trolley, and rail must all be borne by the movement mechanism.
One proposed solution to the foregoing teaches an automatic monorail system including a lowerator mechanism mounted to the monorail above the workstation. A trolley is provided including a workpiece carrier supported thereon by a pair of latches pivotally connected to and carried by the trolley. The lowerator mechanism is operable to lift the workpiece carrier from the trolley latches, and the lowerator lowers the workpiece carrier to the workstation without lowering the trolley or monorail. The lowerator mechanism is mechanically complex. One of the lowerator mechanisms is provided at each workstation. Each lowerator mechanism includes a pair of support rollers mounted in vertically moveable slides, first power actuators for vertically driving the slides, and second power actuators for pivoting the latches. The first power actuators are used first for raising the slide to cause the support rollers to contact the carrier upper support beam and to lift the carrier a short distance off from the trolley latches. The second power actuators can then pivot the trolley latches from under the carrier upper support beam, and the first actuators operate to lower the carrier without any movement of the monorail or the trolley. This complicated lowerator mechanism is mounted to the monorail framework above each workstation requiring increased load carrying capacity for the monorail framework.
Consequently, the need exists for improvements in lowerator devices. Particularly, there exists the need for a lowerator mechanism which meets the efficiency requirements of modern production and assembly lines, and which is simple in operation.
An apparatus according to the present invention includes at least one workpiece carrying trolley that travels along a path between workstations. The workstations can be configured along almost any path that suits the operations to be performed on the carried workpieces. A rail system, having one or more rails, is located with respect to the workstations. For example, a monorail can be suspended from a framework located above the workstations. The monorail can define the path of travel above and through the workstations. The trolleys travel along the monorail between the workstations. The trolleys can be powered by any suitable electrical or mechanical means, such as by power picked up by sliders in contact with electrical conductors mounted to the monorail, or belt driven, or chain driven, or rack and pinion gear driven, or the like.
Each trolley supports a workpiece carrier. The trolley can include at least two vertically extending posts spaced in the direction of the path of travel from one another. The carrier can include a workpiece nest or other workpiece support structure connected to and supported by the posts. The nest or support structure can be designed to support one or more workpieces and can be configured in the manner best suited to the shape of the workpiece and the operations to be performed at the workstation, such as welding multiple workpieces to one another into an assembled product, or subassembly, or other workpiece processing, such as shaping, painting, fastening, gluing, or the like. The trolleys can be driven independently of one another and are controllable to stop at predefined positions, such as at each workstation along the path of travel.
As a trolley approaches a workstation, the carrier engages guide slots or rollers to position the carrier with respect to an actuator. The actuator is mounted to the floor or base of the workstation for moving the carrier with respect to the stationary trolley at the workstation. The actuator according to the present invention is separate from the rail system supporting the trolley. The carrier is lowered by the actuator through a predetermined distance at the workstation, including an additional distance below the workstation nest or tooling, after the weight of the workpiece has been transferred to the nest or tooling, in order to ensure transfer of the workpiece from the carrier to the workstation tooling. The workpiece is positioned in a final location at the workstation by known guides, blocks, and clamps that form part of the workstation tooling. The carrier is guided loosely through predetermined gaps and clearances between vertical surfaces in slide blocks within the posts which permit the carrier to float while descending to enable each workpiece to reach the desired final location.
The present invention provides a lowerator mechanism of simple design and efficient operation. The lowerator mechanism of the present invention can be used in an assembly system of the type including one or more rails defining a path of travel between one or more workstations, and one or more conveyors, for example a trolley-driven carrier, for transporting at least one workpiece along the path of travel. According to the present invention, the conveyor includes a trolley and carrier, the carrier supports the workpiece while moving along the path of travel. The carrier is vertically positionable between raised and lowered positions with respect to the trolley to selectively bring a workpiece into position at a workstation. A latch is provided for securing the carrier to the trolley in the raised position. An actuator or lift is provided at the workstation for positioning the carrier between the raised and lowered positions. Preferably, the lift is support separate from the overhead rail, and most preferably is support from the floor or base of the workstation. The positioning lift defines a path of travel in first and second directions, wherein in the first direction of travel the positioning lift actuates the latch to uncouple the trolley and the carrier and move the carrier into the vertically lowered position, and wherein in the second direction of travel the positioning lift moves the carrier member into the vertically raised position and actuates the latch so as to secure the carrier to the trolley in the raised position.
The present invention provides a lock for preventing unintentional movement of the carrier with respect to the trolley. The carrier can include a pin movable between a locked position and an unlocked position with respect to the latch when the latch is in an engaged position for holding the carrier in a raised position with respect to the trolley. A rotatable catch is mounted with respect to the trolley. When the catch traps the pin in the locked position, the latch is prevented from moving from the engaged position to a disengaged position. An actuator located at each workstation operably moves the catch from the trapped position to a released position allowing the pin to move from the locked position to an unlocked position in response to movement of the latch from the engaged position to the disengaged position. The actuator acts on the catch as the carrier moves toward a stopped position at each workstation. The actuator can be a stationary member or finger engagable with the catch, as the trolley supporting the carrier is approaching the stopped position, to rotate the catch about an axis of rotation from the trapped position to the released position when the trolley and supported carrier are stopped at the workstation. When the trolley and supported carrier move away from the stopped position at each workstation, the catch returns from the released position to the trapped position to move the pin from the unlocked position to the locked position with respect to the latch. The lock defined by the combination of the pin and catch prevents unintentional unlatching of the carrier from the trolley until the combination of actions occur where the catch is moved to the released position and the latch is moved to the disengaged position. The lock according to the present invention can include a lockout pin for preventing unintentional movement of the carrier with respect to the trolley until the lockout pin has been removed. The lockout pin is engagable through a aligned coaxial apertures associated with one of the trolley and the carrier for supporting the lockout pin in a position obstructing free movement of the latch from the engaged position. A movable member can be positioned between the lockout pin and the latch for obstructing movement of the that latch when the lockout pin is located within the coaxial apertures.
According to the present invention, at least one guide member, such as a roller, can be associated with the carrier and engagable with respect to a guide channel positioned at a workstation. The guide channel is located at a workstation for receiving the guide member when the carrier is being moved vertically for guiding movement of the carrier between the raised and lowered positions at the workstation. The guide channel can include an enlarged opening adjacent the top portion for directing the guide member toward the lower portion of the guide channel.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.